1. Field of the Invention
The present invention relates to a steering wheel mounted in a vehicle and, particularly, to a steering wheel equipped with an air bag system. More particularly, the invention relates to a steering wheel including an air bag system supported by horn-switching mechanisms.
2. Description of the Related Art
A known steering wheel of this kind is described, for example, in Japanese Utility Model Unexamined Publication No. 143734/1990 and shown in FIG. 1. This steering wheel, generally indicated by WO, has a wheel main body 1. An air bag system 4 is mounted at the top of the central portion of the wheel main body 1. Each horn-switching mechanism 10 is located between the wheel main body 1 and the air bag system 4. The wheel main body 1 includes part of the steering wheel WO and excludes the air bag system 4 and the horn-switching mechanisms 10.
The air bag system 4 is composed of an air bag 5, an inflator 6, a pad 7, and a bag holder 8. The air bag 5 is folded so that it is capable of inflating. The inflator 6 supplies a gas used to inflate the air bag 5. The pad 7 covers the folded air bag 5. The bag holder 8 holds the air bag 5, the inflator 6, and the pad 7.
The horn-switching mechanisms 10 are located under the bag holder 8 at opposite sides, respectively, of the holder 8 and extend forward and rearward. FIG. 1 is a cross-sectional view of the steering wheel WO, taken in the longitudinal direction and in the front and rear direction.
Each horn-switching mechanism 10 comprises a stationary member 11, a movable member 12, a coil spring 16, and a jawed bolt 19. The stationary member 11 consists of a metal plate and is connected with a metal core 2 forming the steering wheel main body 1. Fixed contacts 14 are mounted to the front and rear ends, respectively, of the stationary member 11. The movable member 12 is made of a metal plate and located above the stationary member 11. Movable contacts 15 are positioned at the front and rear ends, respectively, of the movable member 12. The coil spring 16 is positioned between the movable member 12 and the stationary member 11 and forms a means for biasing the movable member 12 upward. The jawed bolt 19 forms a means for limiting the distance by which the movable member 12 is spaced from the stationary member 11. The jawed bolt 19 is screwed to the metal core 2 from above the movable member 12.
A lead wire (not shown) is connected with each movable member 12 of the horn-switching mechanisms 10 so that the movable member 12 is electrically connected with the positive side of the horn-activating circuit. Each stationary member 11 is electrically connected with the negative side of the horn-activating circuit via the metal core 2.
The fixed contacts 14 and the movable contacts 15 together form a switch main body 13.
Insulating spacers 17, 18 and rubber rings 20 electrically insulate the movable members 12 from the stationary members 11 when they are in contact with both the coil springs 16 and the jawed bolts 19.
Each movable member 12 has a mounting member (not shown) attached thereto permitting the bag holder 8 to be secured with bolts.
In the prior art steering wheel WO, the horn-switching mechanisms 10 are located on opposite sides of, and under, the heavy air bag system 4. That is, the air bag system 4 of the prior art steering wheel WO is swingably supported by the coil springs 16 of the horn-switching mechanisms 10 that are at opposite sides of, and under, the air bag system 4.
When the coil springs 16, used to bias the horn-switching mechanisms 10 of the prior art steering wheel WO, have a low spring constant, the horn-switching mechanisms 10 may be inadvertently activated because the heavy air bag system 4 can easily tilt or swing horizontally due to vibrations of the vehicle.
More specifically, in the prior art steering wheel WO, the air bag system 4 and the movable member 12 are held upwardly by all the coil springs 16. In the illustrated example, four coil springs are used. The position of the resultant center of gravity G of these supported members (the air bag system 4 and the movable member 12) is higher than the coil springs 16 by as much as 30 mm. With the forward coil spring 16F placed at the center of a rotation moment, a rotation moment, Pxc3x97L, acts on the rear coil spring 16B, where P is the force of a rearward swinging movement at the side of the center of gravity G and L is the distance between the center of gravity G and the coil spring 16F in the direction of height. The rotation moment, Pxc3x97L, compresses the coil spring 16B and brings the rear movable contact 15B into contact with the fixed contact 14B. As a result, the switch main body 13B is electrically activated.
Accordingly, the coil springs 16 biasing the horn-switching mechanisms 10 have high spring constants. However, when coil springs having high spring constants are used, as in the coil springs 16, a larger load must be applied to manually activate the horn-switching mechanisms 10. This deteriorates the feel for the horn-switching mechanisms experienced by the driver when the horn-switching mechanisms 10 are operated.
It is an object of the present invention to provide a steering wheel having horn-switching mechanisms which hold a heavy air bag system but give the driver a good feel for the manual operation of the horn-switching mechanisms.
This object is achieved by a steering wheel comprising a horn-switching mechanism and an air bag system held on top of the main body of the steering wheel by the horn-switching mechanism. The horn-switching mechanism comprises a stationary member, a movable member, plural switch main bodies, plural biasing means, and plural limiting members. The stationary member is located under the horn-switching mechanism and connected to the main body of the steering wheel. The movable member is positioned over the horn-switching mechanism and supports the air bag system.
Each switch main body comprises a stationary contact mounted on the stationary member and a movable contact mounted on the movable member. The biasing means are mounted between the stationary member and the movable member and act to bias the movable member upwardly. The limiting members connect the stationary and movable members so that the movable member can move toward the stationary member and limit the distance of the movable member from the stationary member. At least one of the biasing means is located at a height substantially equal to the height of the resultant center of gravity of all components that are biased upwardly.
It is desired that at least one biasing means be located at a height substantially equal to the height of the resultant center of gravity of all components that are biased upwardly and preferably has a vertical center that is substantially coincident with the height of the resultant center of gravity. Also, it is desired that all the biasing means be located at a height substantially equal to the resultant center of gravity of the components that are biased upwardly.
In the steering wheel in accordance with the invention, at least one biasing means is located at a height substantially equal to the height of the resultant center of gravity of all the components that are biased upwardly. Therefore, if one biasing means is not disposed around the height of the resultant center of gravity but is located at the center of the rotation moment, the rotation moment, Pxc3x97L, acts on the biasing means located near the height of the resultant center of gravity, where P is the force of a horizontal swinging movement acting on the center of gravity G of the air bag system and L is the distance between the center of gravity G and the biasing means located near the height of the center of gravity.
This rotation moment, Pxc3x97L, barely compresses the biasing means located near the height of the center of gravity because L is close to zero. Therefore, inadvertent activation of the switch main bodies to operate the horn can be prevented. In addition, the load needed to manually operate the horn-switching mechanisms is reduced because biasing means with lower spring constants may be used or the number of the biasing means may be reduced.
Accordingly, in the steering wheel in accordance with the invention, if a heavy air bag system is mounted to the horn-switching mechanisms, the load applied to manually operate the horn-switching mechanisms may be reduced. This can improve the feel experienced by the operator when the horn-switching mechanisms are operated.
The center of the biasing means is located near the height of the center of gravity of the air bag, system. The above-described distance L can become close to zero by placing, this center of the biasing means at the height of the center of gravity. Consequently, the load required to operate the horn-switching mechanisms may be reduced further by using biasing means having, lower spring constants.
When all the biasing means are located near the height of the center of gravity of the air bag system, all the rotation moments produced about the biasing means can be reduced to nearly zero. In consequence, the load required to manually operate the horn-switching mechanisms may be decreased further by using biasing means of lower spring constants. This may contribute to further improvement of the feel experienced by the operation when operating the horn-switching mechanisms.
Other objects and features of the invention will appear in the course of the description thereof which follows.